This application claims the priority of Korean Patent Application No. 10-2004-0070818, filed on Sep. 6, 2004 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Disclosure
The present disclosure relates to a pyrolysis furnace having an improved gas flowing path controller, and more particularly, to a pyrolysis furnace which controls the flow speed of a gas such as a source gas, uniformly heats the source gas, and controls pyrolysis characteristics of the source gas, thereby manufacturing nanoparticles of uniform size.
2. Description of the Related Art
Methods of manufacturing nanoparticles are mainly divided into chemical wet process methods and vapor deposition methods. A vapor deposition method can be used to freely control the size of nanoparticles compared to other methods, and form nanoparticles at desired locations. Typical vapor deposition methods include a laser ablation method and a pyrolysis method.
In the pyrolysis method, a precursor of a material that is to be processed is used. In more detail, by applying heat to a precursor, which is a source gas, the precursor is pyrolyzed, and monomers in an aerosol state are generated from the pyrolyzed precursor. The monomers are developed to form nanoparticles. Such a pyrolysis method is performed using a simple manufacturing apparatus and process, and the size of the nanoparticles can be easily controlled.
FIGS. 1A and 1B are views of conventional apparatuses for fabricating nanoparticles. FIG. 1A is a schematic view of a pyrolysis furnace 11, an oxidation furnace 12, and a deposition chamber 13 according to the prior art, and FIG. 1B is a cross section of a pyrolysis furnace disclosed in U.S. Pat. No. 6,586,785.
Referring to FIG. 1A, the pyrolysis furnace 11 is fed a source gas 11a of nanoparticles to be formed in the pyrolysis furnace 11 and a carrier gas 11b. The inside temperature of the pyrolysis furnace 11 is maintained at about 900° C. by a heating device (not shown), and thus the source gas 11a is pyrolyzed. When oxidation of the pyrolyzed source gas 11a is required, the source gas is oxidized at a high temperature of about 700° C. or higher inside the oxidation furnace 12. Then, the pyrolyzed and oxidated source gas flows into the deposition chamber 13, thereby depositing nanoparticles on a substrate 13a. 
The pyrolysis furnace 11 may take the form of the pyrolysis furnace illustrated in FIG. 1B. The pyrolysis furnace 11 is fed a source gas 11a and a carrier gas 11b via a source gas tube 15 and a carrier gas tube 14, respectively. The source gas 11a and the carrier gas 11b are mixed and preheated in a ramping region 18a of the pyrolysis furnace 11, and are pyrolyzed in a thermal decomposition region 18b, thereby changing into an aerosol state at a high temperature. Then, the aerosol flows in a direction indicated by an arrow 16a towards an exit 16b and into a deposition chamber (not shown) in which the nanoparticles forming process is performed.
The basic characteristics such as the size, density, and dispersion of the nanoparticles are determined by the density of the source gas 11a, that is, a precursor. When fabricating nanoparticles with a high density, the density of the source gas 11a needs to be high. However, as the density of the precursor increases, the dispersion characteristics of the generated nanoparticles deteriorate.
Such a disadvantage is known to be related to a reaction that occurs when the source gas 11a enters into the pyrolysis furnace 11 for the pyrolysis process. That is, the pyrolysis characteristics of the source gas 11a change according to the amount of time the source gas 11a remains in the ramping region 18a (i.e., a preheating region) after the source gas 11a enters the pyrolysis furnace 11 and before the pyrolysis occurs.
FIG. 2 is a graph illustrating the temperature distribution of a gas injected into the pyrolysis furnace 11 illustrated in FIG. 1B. In the graph, it can be seen that there is a great change in the temperature in the ramping region 18a when the source gas 11a and the carrier gas 11b are supplied to the pyrolysis furnace 11. If the time the gas spends in the ramping region 18a increases due to the temperature change, the size of a precursor, which is the source gas 11a, changes, thereby deteriorating the dispersion characteristics of nanoparticles.
To form nanoparticles of uniform size, the source gas 11a and the carrier gas 11b must be quickly and sufficiently mixed in uniform densities before pyrolysis occurs, and the mixed gases must have a uniform density distribution throughout the pyrolysis furnace 11. However, a conventional pyrolysis apparatus and process does not satisfy these requirements.